Optical fiber cable and an associated method of manufacture

Abstract

The present invention relates to an optical fiber cable, in particular for a distribution network, and comprising an assembly of optical fibers, wherein each of the optical fibers has a mode field diameter lying in the range 7 μm to 9 μm at around 1550 nm, and a cutoff wavelength less than or equal to 1.35 μm, and wherein the optical fibers are assembled together in the cable by being twisted around one another or around a reinforcing element, or by being disposed lengthwise.

We claim: 
     
       1. An optical fiber cable comprising: a plurality of optical fibers, each fiber having an optical core surrounded by optical cladding, each of said optical fibers being provided over said optical cladding with a substantially hermetic coating and including over said hermetic coating a coating of plastics material;   said cable further including an outer protective sheath of plastics material surrounding said optical fibers;   wherein each of said optical fibers has a mode field diameter lying in the range 7 μm to 9 μm at around 1550 nm, and a cutoff wavelength that is less than or equal to 1.35 μm, and   wherein said optical fibers are assembled together in said cable by being twisted around one another.   
     
     
       2. A cable according to claim 1, wherein said plastics coating includes identification information for identifying each fiber. 
     
     
       3. A cable according to claim 2, wherein said identification information corresponds to a color code. 
     
     
       4. A cable according to claim 1, wherein the optical fibers are assembled together in bundles. 
     
     
       5. A cable according to claim 1, wherein the optical fibers are assembled together in concentric layers. 
     
     
       6. A cable according to claim 1, wherein optical fibers are assembled together in a helical pitch. 
     
     
       7. A cable according to claim 1, wherein the optical fibers are assembled together in an SZ type assembly pitch. 
     
     
       8. A cable according to claim 1, wherein the optical fibers are multi-core fibers. 
     
     
       9. A cable according to claim 1, wherein said hermetic coating of each fiber comprises a deposit of carbon on the optical cladding. 
     
     
       10. A cable according to claim 1, wherein said hermetic coating of each fiber comprises titanium oxide based doping of said optical cladding. 
     
     
       11. A method of making an optical fiber cable according to claim 1, comprising the following steps: making optical fibers having a mode field diameter lying in the range 7 μm to 9 μm at around 1550 nm, and a cutoff wavelength that is less than or equal to 1.35 μm;   treating each fiber to make it substantially hermetic;   making a thin plastics coating that is applied directly on each previously-treated fiber;   assembling the fibers that have been treated and coated in this way; and   applying a sheath to the assembly.   
     
     
       12. An optical fiber cable comprising: a plurality of optical fibers, each fiber having an optical core surrounded by optical cladding, each of said optical fibers being provided over said optical cladding with a substantially hermetic coating and including over said hermetic coating a coating of plastics material;   said cable further including an outer protective sheath of plastics material surrounding said optical fibers;   wherein each of said optical fibers has a mode field diameter lying in the range 7 μm to 9 μm at around 1550 nm, and a cutoff wavelength that is less than or equal to 1.35 μm, and   wherein said optical fibers are assembled together in said cable by being twisted around a reinforcing element.   
     
     
       13. An optical fiber cable comprising: a plurality of optical fibers, each fiber having an optical core surrounded by optical cladding, each of said optical fibers being provided over said optical cladding with a substantially hermetic coating and including over said hermetic coating a coating of plastics material;   said cable further including an outer protective sheath of plastics material surrounding said optical fibers;   wherein each of said optical fibers has a mode field diameter lying in the range 7 μm to 9 μm at around 1550 nm, and a cutoff wavelength that is less than or equal to 1.35 μm, and   wherein said optical fibers are assembled together in said cable by being disposed lengthwise.